Medical imaging devices, such as, for example, computer tomographs or fluoroscopy devices, use ionizing radiation in order to produce analyzable image data. A fundamental aim is, wherever possible, to expose patients to only such a radiation dose needed to be able to guarantee an adequate image quality. In this context, the radiation dose to be applied and the image quality are in a competing relationship so that the radiation dose is to be determined in each case through consideration of both aspects, which hinders an automatic control of the radiation dose. The dose determination is an important preparatory act in the planning, performance, and/or control of the device in a radiotherapeutic or nuclear medical procedure.
Along with the consideration of how much of a dose reduction is achievable without having to accept interfering losses in image quality, the user is confronted with a multiplicity of examination parameters. Dose measurements are modality-specific measurement methods or estimation methods (e.g., for CT: volume CT dose index (CTDIvol) and dose length product (DLP); for fluoroscopy: dose area product (DAP), kerma area product (KAP), cumulative air kerma (CAK) and entrance surface dose (ESD), etc.). The effects of changes in one or more of these parameters on the image quality and dose often cannot be evaluated in a straightforward manner by the user. Moreover, there are manufacturer-specific parameters, the technical background of which may not be known in detail to the user. Dose optimization is also dependent on the type of imaging examination (e.g., modality employed and type of examination, such as thorax CT and abdomen CT).
Given this complexity, in known methods, radiologists may rely on heuristics and empirical values in the creation of examination protocols. However, the quality assurance measures usable here are unfortunately very restricted. It is thus possible to implement institution-related quality assurance measures whereby, for example, radiologists define institution-related standards for examination protocols based on published studies of leading centers. In addition, the use of ionizing radiation is also controlled in regulatory standards (e.g., the X-ray Ordinance) and by external quality assurance authorities (e.g., a medical authority within the framework of constancy tests). There are also quality assurance programs under the responsibility of medical societies for imaging-controlled interventional procedures (e.g., percutaneous transluminal angioplasty (PTA) of leg arteries) or the inter-institutional comparison of diagnostic examinations (e.g., RSNA Dose Registries for CT examinations in the USA). However, all of these measures either use heuristics, concentrate on specific examination types or the evaluation of the dose (e.g., distribution) on the basis of phantom-based measurements (e.g., model-based dose measurements under controlled conditions that do not take into account the patient constitution and take only restricted account of anatomical structure details).
On this basis, a patient-oriented and patient-specific and case-specific prediction and optimization of examination parameters for dose optimization is possible to a restricted extent only or even not possible at all. Heuristics allow the dose to be influenced within specific orders of magnitudes, e.g., intervals are often indicated for examination parameters or fixed protocols that do not take any account or only take insufficient account of the individual patient constitution, the hardware and software used and the special characteristics of the examination process. An act in quality assurance may include in the avoidance of outliers, e.g., of examinations in which an obviously excessively high dose is used and not in a fine-granularity dose optimization. Due to the high complexity of the relevant parameters, it is not possible for many examination variants simply to refer to publications that describe specifically adapted solutions for the current problem (e.g., complex combination of examination, issues involved, patient constitution, and device type).
In the prior art, a method is known from U.S. Patent Publication No. 2012/0148131 for estimating the radiation applied to a patient radiation during a CT examination on the basis of model-based phantom bodies. However, this procedure has the disadvantage that patient-specific and device-specific dose calculations are not possible. Neither does this publication address the targeted control of an imaging device with respect to the dose values.
On the basis of this prior art, it is the object to provide an automatic dose control system for imaging devices that evaluates the image quality of a plurality of previous examinations. In this context, the previous examinations may be targeted at the same anatomical region. Overall, this may improve the quality of an imaging examination and reduce the radiation intensity for the patient while maintaining an adequate image quality.